Blade shrouding



y l944v- H. P. DAHLSTRAND f 2,350,309

BLADE SHROUDING Filed Sept. 12, 1940 Patented May 30, 1944 BLADESHROUDING Hans P. Dahlstrand, Wauwatosa, Wis., assignor toAllis-Chalmers Manufacturing. Company, Milwaukee, Wis, a corporation ofDelaware Application September 12, 1940, Serial No. 356,411

5 Claims.

This invention relates to blade shrouding and more particularly to a.method of forming a builtup shroud and seal structure for the tipportions of turbine blades.

The primary object of this invention is to provide a method of formingan improved built-up shroud and seal structure for turbine blades whichis extremely durable and cheap to manufacture.

Another object of this invention is to provide a method of forming animproved shroud and seal structure for turbine blades in which theshroud and seal structure is formed from a plurality of stampings whichare welded together and to the blade tip to form an integral shroud andseal structure having at least three sealing flanges.

A further object of this invention is to provide an improved method ofconstructing a built-up welded shroud and seal structure for turbineblades.

The invention accordingly consists of the method of construction and ofthe various features of construction, combinations of elements andarrangements of parts as more fully pointed out in the appended claimsand in the detailed description, in which:

Fig. 1 is a partial sectional view of a turbine spindle and statorhaving coacting blades em-' bodying the invention;

Fig. 2 is a plan view of a portion of a moving blade row taken on lineIIII of Fig. 1 with a part of the shroud structure broken away;

Fig. 3 is a side view of the top portion of one of the blades shown inFig. 2 with the shroud removed;

Fig. 4 is a plan view of the blade shown in Fig. 3;

Fig. 5 is a side view, partly in section, of the type of blade shown inFigs. 3 and 4 with the shroud and sealin means attached thereto;

Fig. 6 is a side view of the top portion-of a blade illustrating amodified construction;

Fig. '7 is a plan view of the blade shown in Fig.6;

Fig. 8 is a side view, partly in section, of the type of blade shown inFigs. 6 and '7 with the shroud and sealing means attached thereto;

Fig. 9 is a perspective view of a segmental group of blades with theshroud removed; and

Fig. 10 is a vertical section illustrating apparatus for temporarilyholding the shroud and sealing structure on a blade or on a group ofblades preparatory to Welding the structure thereto.

mass of the said shroud member.

Referring to Fig. 1 of the drawing, it is seen that the inventionisshown as applied to the stationary and moving blades l and 2,respectively, of a turbine structure comprising a stator 3 and a rotor4. The individual blades l and 2 are provided with conventional root orbase portions 6 and 1, respectively, which are removably secured incirc-umferentially extending grooves 8 and 9 in the stator and rotor,respectively, in the usual manner. The manner in which the blades aresecured in the turbine structure forms no part of this invention andsince any desired form of securing means may be used, a furtherdescription in this connection is not necessary for a completeunderstanding of "the present invention.

Referring to Figs. 2-5 inclusive, it is seen that the tip portions ofthe blades 2 are shaped to provide a stepped projection comprising arelatively short'porti-on II which is made approximately equal in lengthto the thickness of the shroud member to be secured to the blade tip anda relatively long portion [2 which is made approximately equal in lengthto twice the thick- The shrouding and sealing means comprises a firstmember having a base or shroud portion l3 and an upstanding sealingflange l4 and a, second channel shaped member having a base or Webportion N3 of less width than the base portion l3 of the first memberand presenting when mounted on the tip portion of a blade a pair oflaterally spaced upstanding sealing flanges H. The base portion I3 ofthe first member is provided with an opening l8 adapted to snuglyreceive the stepped projection and the base member 16 0f the secondmember is also provided with an opening l9 adapted to snugly receive therelatively long portion l2 of the said projection. The Width of the baseportion l3 of the first member is such that when the first member ispositioned on the blade tip as shown in Fig. 5, an edge portion of saidbase member extends beyond and overhangs the edge of the blade therebyproviding a laterally extending sealing flange 2|.

The dimensions of the first and second members, the arrangement of theopenings [8 and I9 therein, respectively, and the dimensions and thearrangement ofthe stepped projection are such that when the first andsecond members are positioned on the tip portion of a blade in the ordernamed, the shrouding and sealing means are arranged as shown in Fig. 5.The thickness of the baseor web portion l6 of the second member' issubstantially the same as the thickness of the base or shroud portion 13of the first member. Consequently, since the length of the portions IIand I2 of the stepped projection is approximately equal to the thicknessand to twice the thickness of the shroud portion l3, respectively, itshould be obvious that when the first and second members are positionedon the blade as shown in Fig. 5, the top of the portion II will be nearlflush with the top surface of the base or shroud portion l3 and the topof the portion 12 will be nearly flush with the top surface of the baseor web portion I6. Therefore, when the first and second members are thuspositioned on the blade tip, all that remains to be done in order toobtain a permanent structure is to weld the base portions of the firstand second members to,

the juxtapositioned portions H and I2 of the stepped projection asindicated in Figs. 1, 2 and 5. When the first and second members aredimensioned to span a series of blades as indicated in Fig. 2, the saidmembers are positioned on and welded to the blades after they have beenmounted on'the turbine rotor or stator. Any suitable means may beemployed for holdin said members in their proper assembled relationduringthe welding operation and in this connection apparatus somewhatsimilar to that shown in Fig. has been found entirely satisfactory.

The modified arrangement shown in Figs. 6-8, inclusive, in which likenumerals are used to designate thesame or similar parts, differs fromthat shown in Figs. 1-5, inclusive, in that the tip portion of the blade2 is provided with two laterally spaced upstandin projections 22 and 23,and in that the base or shroud portion [3 of the first member isprovided with two laterally spaced openings 24 and 26 adapted to snuglyreceive the projections 22 and 23, respectively. The length of theprojection 22 is approximately equal to the thickness of the base orshroud portion I3 of the first member and the length of the projection23 is approximately equal to the combined thickness of the base orshroud member iii of the first member and the base or web portion I5 ofthe second member as best shown in Fig. 8. The first and second memberscomprising the shrouding and sealing means are positioned and held inposition on the tip portions of the blades and welded thereto in exactlythe same manner as set forth in connection with the description of Figs.1-5, inclusive, and a repetition of this procedure is not deemednecessary for a complete understanding of the invention. The resultantstructure affords all of the advantages with respect to assembly andstrength'inherent in the preferred construction shown in Figs. 1-5,inclusive, but is less desirable in that shaping spaced projections ismore difficult and therefore more costly than shaping the steppedprojection employed in the preferred construction.

Fig. 9 shows a unitary segmental blade group 21 in which the tip portionof each blade 28 is provided with a stepped projection comprising eachsuch group of blades is of course identical to that disclosed inconnection with Figs. 1-5, inclusive, but in this construction, thefirst and second members comprising the shrouding and sealing means arepreferably secured to the individual groups before they are mounted onthe turbin rotor or stator.

Fig. 10 illustrates a suitable jig or fixture 3| for holding the firstand second members in their proper assembled relation on the tipportions of the blades 28 during the welding operation. The jig 3|comprises a base 32 having a portion 33 adapted to receive thereon thebase member 29 of a segmental blade group, a pair of top members 34 and36 having edge portions 31 and 38, respectively, adapted to coact withthe flanges l4 and 2! of the first member and with the flanges ll of thesecond member, spacing members 39 and M, and clamping bolts 42 and 43 bymeans of which the top members 34 and 36 may be drawn toward the base 32thereby firmly holding the first and second members in their assembledrelation on the tip portions of the blades. The jig 3! is merelyillustrative of a commercial ly practical construction adapted forcarrying out the present invention with respect to segmental bladegroups and it should be understood that any other suitable jig orfixture may be used if it is so desired.

Referring again to Fig. 1, it is seen that the shrouding and sealingmeans applied to the stationary blades I differs from that employed onthe moving blades 2 in that the first member is channel shaped and inthat the second member is L-shaped. The web portion 44 of the firstmember constitutes the shroud portion and the channels 46 sealingflanges. The base member 4'! of the second member is of less width thanthe web portion 44 of the first member and is adapted to be positionedon the base or web portion 44 of the first member so that the sealingflange 48 is disposed approximately midway between the channels 46 onthe first member. The first and second members are positioned on the tipportion of the stationary blades and secured thereto in exactly the samemanner as disclosed in connection with the moving blades 2 and thereforea further description in this connection is deemed unnecessary. In allmodifications, the length of the centrally disposed sealing flange ispreferably made higher than the height of the other sealing flanges andthe opposed surfaces of the rotor and stator are provided with coactinggrooves 49 and 5|, respectively.

From a consideration of the foregoing and the accompanying drawing, itshould be obvious that in accordance with this invention the end of ablade or the ends of a group of blades can be readily shrouded andprovided with an intermediate or centrally disposed upstanding'andcircumferentially extending sealing'flange I! (such a construction isimpractical with blades having a centrally disposed tenon of the typeheretofore employed) without in any manner weakening the connectionbetween the end of the blade and the superimposed shroud and sealstructure. In fact, the disclosed construction is much stronger than thetenoned constructions heretofore employed since, as clearly shown, ashroud and seal structure embodying the invention is secured or attachedto the end of the blade by an effective bond area which is substantiallyequal to the area of the blade end, thereby materially reducing, and insome instances, entirely eliminating the cantilever effect produced bycantrifugal force acting on the free edges of shroud and seal stripswhich are secured to the end of a blade by a centrally disposed tenon.

Shrouding and sealing structures with multiple spaced sealing flangescan be readily built up in accordance with this invention more cheaplythan has heretofore been possible with the prior art methods and thestructures produced in accordance with this invention have excellentphysical properties with respect to stress resistance and with respectto corrosion and erosion resistance. The invention is applicable to alltypes of turbine blading with respect to which it is necessary to employa shrouding and sealing means and while the invention has been disclosedin connection with shrouding and sealing means adapted to span a seriesof blades, it should be understood that the invention is not in anymanner limited to the exact mode of construction or to the exactconstructions herein shown and described as various modifications withinthe scope of the appended claims may occur to persons skilled in theart.

It is claimed and desired to secure by Letters Patent:

1. A method of forming a combined shroud and seal structure on the endof a blade which comprises providing a blade having on said end andadjacent one edge thereof a first upstanding portion and having in saidend adjacent its other edge a second upstanding portion of materiallygreater length than said first portion, placing on said end of the bladea first element of said structure apertured to receive said upstandingportions and having a thickness approximately equal to the length ofsaid first portion, superimposing on said first element, a secondelement of said structure including a base apertured to receive saidsecond portion and having a thickness approximately equal to the exposedlength of said second portion and a width sufiiciently less than thewidth of said first element to leave exposed a part of said end of saidfirst portion, and securing said first element and the base of saidsecond element to the exposed parts of said first and second portions,respectively.

2. A method of forming a combined shroud and seal structure on the endof a blade member presenting in spaced upstanding relation, a firstportion and a second portion of materially greater length than saidfirst portion which comprises placing on said end of the blade a shroudelement apertured to receive said upstanding portions and having athickness approximately equal to the length of said first portion,superimposing on said shroud strip a seal element including a baseapertured to receive said second portion and having a thicknessapproximately equal to the exposed length of said second portion and awidth sufiiciently less than the width of said shroud element to leaveexposed a part of the end of said first portion, and securing saidshroud element and the base of said seal element to the exposed parts ofsaid first and second portions, respectively.

3. A method of forming a combined shroud and seal structure on the endof a blade member presenting an upstanding stepped projection having itslower step disposed adjacent one edge of said blade and having itshigher step disposed adjacent the other edge of said blade, whichcomprises placing on said end of the blade a shroud element apertured toreceive said upstanding projection and having a thickness approximatelyequal to the height of said lower step, superimposing on said shroudstrip a seal element including a base apertured to receive said higherstep and having a thickness approximately equal to the height of saidhigher step and a width sufficiently less than the width of said shroudelement to leave exposed a part of the top of said lower step, andsecuring said shroud element and the base of said seal element to theexposed parts of said lower and higher steps, respectively.

4. A method of forming a combined shroud and seal structure on the endof a blade which comprises providing a blade having on one end thereofjuxtapositioned short and long tenon portions, placing on said one endof the blade a first element of said structure apertured to receive andexpose the end parts of said short and long tenon portions,superimposing on said first element a second element of said structureincluding a base apertured to receive and expose the end part of saidlong tenon portion and having a width sufiiciently less than the widthof said first element to leave exposed a part of the end of the shorttenon portion, and securing saidfirst element and the base of saidsecond element to the exposed end parts of said short and long tenonportions, respectively.

5. A method of forming a combined shroud and seal structure on the endof a blade which comprises providing a blade having on one end thereofjuxtapositioned short and long tenon portions, placing on said one endof the blade a first element of said structure apertured to receive andexpose the end parts of said short and long tenon portions and having athickness approximately equal to the length of said short tenon portion,superimposing on said first element a second element of said structureincluding a base apertured to receive and expose the end part of saidlong tenon portion and having a thickness approximately equal to theexposed length of said long tenon portion and a width sufiiciently lessthan the width of said first element to leave exposed a part of the endof the short tenon portion, and fusibly uniting said first element andthe base of said second element to the exposed end parts of said shortand long tenon portions, respectively.

HANS P. DAI-ILSTRAND.

